In general, a liquid container such as an ink cartridge which accommodates liquid therein as a liquid source is installed in a liquid ejecting apparatus which ejects liquid such as ink from ejection nozzles like an ink jet printer. The liquid container is detachably installed to the liquid ejecting apparatus, and the liquid is supplied to the liquid container from a liquid supply port. When the liquid in the liquid container has been expended, a new liquid container can replace the liquid container.
With the purpose of informing a user of replacement time of the liquid container (when the liquid in the liquid container has been expended), technology that a rectangular prism is provided on a bottom portion of the liquid container, and the liquid in the liquid container can be detected by using a light emitting element and a light receiving element provided in the liquid ejecting apparatus main body has been proposed (For example, PTL 1). In the technology, light which enters an incident surface of the prism from the light emitting element to, and is transmitted into the liquid container in a state in which the liquid in the liquid container is sufficient. On the other hand, when the liquid in the liquid container is consumed and the prism is exposed from the liquid, the light of the light emitting element which enters the incident surface of the prism is reflected by a boundary surface between the prism and air in the liquid container to reach the light receiving element. Accordingly, it is possible to detect the remaining liquid amount in the liquid container based on whether the light receiving element receives the light of the light emitting element.
In the liquid container disclosed in PTL 1, a contact portion is provided on a side surface of the liquid container, and when the liquid container is mounted in the liquid ejecting apparatus, the contact portion of the liquid container and a connection unit of the liquid ejecting apparatus main body side are electrically connected to each other.